WO2016130780A1 - Ac amplifier output impedance reduction - Google Patents

Ac amplifier output impedance reduction Download PDF

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Publication number
WO2016130780A1
WO2016130780A1 PCT/US2016/017515 US2016017515W WO2016130780A1 WO 2016130780 A1 WO2016130780 A1 WO 2016130780A1 US 2016017515 W US2016017515 W US 2016017515W WO 2016130780 A1 WO2016130780 A1 WO 2016130780A1
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WO
WIPO (PCT)
Prior art keywords
power supply
stage
output
inductor
switching
Prior art date
Application number
PCT/US2016/017515
Other languages
French (fr)
Inventor
Kevin Cobley
Original Assignee
Snaptrack, Incorporated
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by Snaptrack, Incorporated filed Critical Snaptrack, Incorporated
Publication of WO2016130780A1 publication Critical patent/WO2016130780A1/en

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Classifications

    • H—ELECTRICITY
    • H03—ELECTRONIC CIRCUITRY
    • H03F—AMPLIFIERS
    • H03F1/00—Details of amplifiers with only discharge tubes, only semiconductor devices or only unspecified devices as amplifying elements
    • H03F1/02—Modifications of amplifiers to raise the efficiency, e.g. gliding Class A stages, use of an auxiliary oscillation
    • H03F1/0205—Modifications of amplifiers to raise the efficiency, e.g. gliding Class A stages, use of an auxiliary oscillation in transistor amplifiers
    • H03F1/0211—Modifications of amplifiers to raise the efficiency, e.g. gliding Class A stages, use of an auxiliary oscillation in transistor amplifiers with control of the supply voltage or current
    • H03F1/0216—Continuous control
    • H03F1/0222—Continuous control by using a signal derived from the input signal

Definitions

  • the present invention relates to power supplies incorporating switching stages, and particularly but not exclusively to envelope tracking power supplies for radio frequency power amplifiers.
  • An envelope tracking power supply for a radio frequency power amplifier is an example of a power supply incorporating switches.
  • the switches in a switching stage of such a power supply switch between different supply levels in order to generate an output modulated power supply.
  • the switching introduces noise into the signal at the output of the power supply.
  • a power supply including a switching stage and configured to adapt the generated power supply signal to remove at least some of the switching currents in that signal.
  • the power supply may further comprise a circuit configured to sense the switching currents in the power supply.
  • the power supply may include a switching stage, a correction stage and a combiner, the combiner configured to combine the outputs of the switching stage and the correction stage to provide the generated power supply, wherein the circuit is connected to the output of the correction stage.
  • the combiner may include an inductor, the circuit being configured to sense the switching currents in the inductor.
  • the circuit may include a series connection of a resistor and a capacitor between the combiner and ground.
  • the power supply may further comprise a connection from the junction of the resistor and capacitor to the correction stage.
  • the correction stage may include an amplifier and is configured to modify the correction stage output in dependence on the connection.
  • the correction stage may be configured to modify the correction stage output further in dependence on a feedback connection from the output of the correction stage.
  • the combiner may comprise an inductor having one terminal connected to the output of the switching stage and a second terminal connected to the output of the correction stage, the circuit being connected to the second terminal of the inductor and the power supply signal being generated at the second terminal of the inductor.
  • the combiner may comprise an inductor and a capacitor, the inductor having one terminal connected to the output of the switching stage and another terminal connected to one terminal of the capacitor, and the capacitor having another terminal connected to the output of the correction stage, the circuit being connected to the second terminal of the capacitor and the power supply signal being generated at the second terminal of the inductor.
  • FIG. 1 illustrates an example power supply including a switching stage
  • FIG. 2 illustrates a plot of inductor current for an arrangement of FIG. 1 using an inductor in a combiner
  • FIG. 3 illustrates an arrangement of FIG. 1 to obtain information on switching currents in the inductor
  • FIG. 4 illustrates an improved power supply including a switching stage
  • FIG. 5 illustrates a further improved power supply including a switching step
  • FIG. 6 illustrates a yet further improved power supply including a switching stage.
  • the invention is now described with reference to particular examples and with reference in particular to an example of a switched power supply stage of an envelope tracking modulated power supply for radio frequency amplifier.
  • the invention is not limited to such an example implementation.
  • an exemplary modulated power supply stage 28 provides a modulated supply signal on line 8 to a power amplifier (PA) 2.
  • the PA 2 receives a radio frequency (RF) input signal on line 4 and generates an RF output signal on line 6.
  • the PA 2 represents a load being driven by the modulated power supply stage 28.
  • RF radio frequency
  • the exemplary modulated power supply stage 28 includes a switching stage or switcher 10, a correction stage 16, and a combiner 30.
  • the combiner 30 includes an inductor 14 and a capacitor 26.
  • the switching stage 10 generates a switcher output signal on line 12.
  • Line 12 is connected to one terminal of the inductor 14.
  • the other terminal of the inductor 14 is connected to the output line 8.
  • the correction stage 16, which includes a correction amplifier 18, generates a correction signal on line 24.
  • Line 24 is connected to one terminal of a capacitor 26.
  • the other terminal of the capacitor 26 is connected to the output signal on line 8.
  • the inductor 14 and capacitor 26 together form the combiner 30 which combines the output signals from the switching stage and the correction stage to produce the modulated supply signal on line 8.
  • a reference signal representing the desired output signal level is provided on line 21 to the switching stage 10 and to the correction stage 16.
  • the reference signal on line 21 is provided to the correction stage on line 20 and forms one input to the correction amplifier 18.
  • the other input to the correction amplifier 18 is a feedback signal, with the output signal of the correction amplifier on line 24 being fed back to its input as denoted by line 19.
  • Modulated power supply stages are designed to have low impedance outputs in order to minimise the noise current in their output signal.
  • a switcher current, denoted iswitcher, flowing in the inductor 14 contributes to the noise current in the output signal.
  • FIG. 2 illustrates a plot 7 of the total current flowing in inductor 14, plotted against frequency.
  • the plot 7 includes a portion of wanted signal, a portion associated with the self-resonance of the inductor, and a portion as denoted by reference numeral 9 which is distorted due to the ripple current associated with the switching current iswitcher from the switching stage 10.
  • the dashed line 5 continuing from the plot 7 represents the ideal wanted signal in which the ripple current and the current due to the self-resonance are eliminated.
  • a modification is proposed to reduce the ripple current.
  • FIG. 3 shows a modification to the arrangement of FIG. 1, in which a circuit 44 is connected to the output of the correction stage 16.
  • the circuit 44 includes a capacitor 42 having a first terminal connected to the line 24, and a resistor 40 having a first terminal connected to the second terminal of the capacitor 42 and a second terminal connected to electrical ground.
  • the current flowing in the circuit 44 provides information on the switching current flowing in the inductor 14. This information can be used to improve the switched power supply of FIG. 1 to remove at least some of the switching current in the generated power supply signal.
  • FIG. 4 illustrates a further modification to the arrangement of FIG. 3.
  • a signal line 50 is connected from the circuit 44 - the connection point of the resistor 40 with the capacitor 42 - to the correction stage 16.
  • the correction stage 16 thus receives, with this connection, information about the current flowing in the conductor 14 from the circuit 44.
  • the signal on line 50 is a feedback signal to the correction stage.
  • the feedback signal to the correction stage utilises the characteristic that the voltage at the node between the resistor 40 and capacitor 42 in the circuit 44 provides information that is not otherwise available in the modulated power supply.
  • the feedback provided by the signal on line 50 can be made fast and can operate at high frequencies.
  • FIG. 5 shows a specific arrangement in which the feedback of the correction stage is used together with the feedback of the information on the switching current flowing in the inductor 14.
  • the correction stage 16 is shown as additionally including an amplifier 54 and a feedback stage 52.
  • the correction amplifier 34 receives the feedback signal on line 50, and receives the output of the amplifier 54.
  • the amplifier 54 receives the reference signal on line 20, and the output of the correction amplifier 34 fed back through a feedback stage 52.
  • the feedback stage 52 applies any necessary attenuation to the feedback signal before it is applied to the amplifier 54.
  • the feedback stage 52 and the amplifier 54 provide, in the arrangement of FIG. 5, the functionality of the feedback provided by the signal on line 19 in the earlier figures.
  • the feedback provided on signal line 50 allows the signal generated by the correction stage 16, in the FIG. 5 arrangement the signal generated by the amplifier 34, to be adjusted to reduce the current ripple due to switching in the output signal, and hence lower the output impedance of the modulated power supply stage 28.
  • FIG. 6 shows an alternative arrangement.
  • the combiner 36 of the FIG. 6 arrangement does not include a capacitor.
  • the capacitor of the combiner of any previous figures may be eliminated in certain implementations, and FIG. 6 illustrates how the advantageous feedback connection may still be utilised even when the capacitor of the combiner is not implemented.
  • the switching stage and the correction stage are each shown as receiving a common reference signal. In embodiments they may receive different reference signals. In embodiments they may not both receive reference signals.
  • the reference signal may indicate the ideal output signal.
  • the reference signal may be the envelope of the RF input signal on line 4.
  • the circuit 44 may be provided for other purposes, and the invention may take advantage of the provision of this circuit for other purposes, to provide information which can be used to improve the switched power supply without adding additional circuit components, and just adding the connection of line 50.
  • the circuit 44 may be provided to suppress resonance as disclosed in WO 2005/081399.

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  • Engineering & Computer Science (AREA)
  • Power Engineering (AREA)
  • Amplifiers (AREA)

Abstract

There is provided a power supply including a switching stage and configured to adapt the generated power supply signal to remove at least some of the switching currents in that signal.

Description

AC AMPLIFIER OUTPUT IMPEDANCE REDUCTION
CROSS-REFERENCE TO RELATED APPLICATIONS:
This application claims priority to GB Application No. 1502248.6, filed February 11, 2015.
BACKGROUND TO THE INVENTION:
Field of the Invention:
The present invention relates to power supplies incorporating switching stages, and particularly but not exclusively to envelope tracking power supplies for radio frequency power amplifiers.
Description of Related Art:
An envelope tracking power supply for a radio frequency power amplifier is an example of a power supply incorporating switches. The switches in a switching stage of such a power supply switch between different supply levels in order to generate an output modulated power supply.
The switching introduces noise into the signal at the output of the power supply.
For efficient power supplies it is advantageous in at least some scenarios to minimise any noise associated with such switching, in order to avoid such noise being present on the modulated power supply itself.
It is an aim of the present invention to provide a technique to reduce the switching noise caused by switching in a switched power supply.
SUMMARY OF THE INVENTION:
There is provided a power supply including a switching stage and configured to adapt the generated power supply signal to remove at least some of the switching currents in that signal.
The power supply may further comprise a circuit configured to sense the switching currents in the power supply.
The power supply may include a switching stage, a correction stage and a combiner, the combiner configured to combine the outputs of the switching stage and the correction stage to provide the generated power supply, wherein the circuit is connected to the output of the correction stage. The combiner may include an inductor, the circuit being configured to sense the switching currents in the inductor.
The circuit may include a series connection of a resistor and a capacitor between the combiner and ground.
The power supply may further comprise a connection from the junction of the resistor and capacitor to the correction stage.
The correction stage may include an amplifier and is configured to modify the correction stage output in dependence on the connection.
The correction stage may be configured to modify the correction stage output further in dependence on a feedback connection from the output of the correction stage.
The combiner may comprise an inductor having one terminal connected to the output of the switching stage and a second terminal connected to the output of the correction stage, the circuit being connected to the second terminal of the inductor and the power supply signal being generated at the second terminal of the inductor.
The combiner may comprise an inductor and a capacitor, the inductor having one terminal connected to the output of the switching stage and another terminal connected to one terminal of the capacitor, and the capacitor having another terminal connected to the output of the correction stage, the circuit being connected to the second terminal of the capacitor and the power supply signal being generated at the second terminal of the inductor.
BRIEF DESCRIPTION OF THE FIGURES:
The invention is now described by way of reference to the drawings, in which: FIG. 1 illustrates an example power supply including a switching stage;
FIG. 2 illustrates a plot of inductor current for an arrangement of FIG. 1 using an inductor in a combiner;
FIG. 3 illustrates an arrangement of FIG. 1 to obtain information on switching currents in the inductor;
FIG. 4 illustrates an improved power supply including a switching stage;
FIG. 5 illustrates a further improved power supply including a switching step; and
FIG. 6 illustrates a yet further improved power supply including a switching stage. DESCRIPTION OF PREFERRED EMBODIMENTS:
The invention is now described with reference to particular examples and with reference in particular to an example of a switched power supply stage of an envelope tracking modulated power supply for radio frequency amplifier. The invention is not limited to such an example implementation.
With reference to FIG. 1 an exemplary modulated power supply stage 28 provides a modulated supply signal on line 8 to a power amplifier (PA) 2. The PA 2 receives a radio frequency (RF) input signal on line 4 and generates an RF output signal on line 6. The PA 2 represents a load being driven by the modulated power supply stage 28.
The exemplary modulated power supply stage 28 includes a switching stage or switcher 10, a correction stage 16, and a combiner 30. The combiner 30 includes an inductor 14 and a capacitor 26. The switching stage 10 generates a switcher output signal on line 12. Line 12 is connected to one terminal of the inductor 14. The other terminal of the inductor 14 is connected to the output line 8. The correction stage 16, which includes a correction amplifier 18, generates a correction signal on line 24. Line 24 is connected to one terminal of a capacitor 26. The other terminal of the capacitor 26 is connected to the output signal on line 8. The inductor 14 and capacitor 26 together form the combiner 30 which combines the output signals from the switching stage and the correction stage to produce the modulated supply signal on line 8. A reference signal representing the desired output signal level is provided on line 21 to the switching stage 10 and to the correction stage 16. The reference signal on line 21 is provided to the correction stage on line 20 and forms one input to the correction amplifier 18. The other input to the correction amplifier 18 is a feedback signal, with the output signal of the correction amplifier on line 24 being fed back to its input as denoted by line 19.
Modulated power supply stages are designed to have low impedance outputs in order to minimise the noise current in their output signal. A switcher current, denoted iswitcher, flowing in the inductor 14 contributes to the noise current in the output signal.
FIG. 2 illustrates a plot 7 of the total current flowing in inductor 14, plotted against frequency. The plot 7 includes a portion of wanted signal, a portion associated with the self-resonance of the inductor, and a portion as denoted by reference numeral 9 which is distorted due to the ripple current associated with the switching current iswitcher from the switching stage 10. The dashed line 5 continuing from the plot 7 represents the ideal wanted signal in which the ripple current and the current due to the self-resonance are eliminated.
A modification is proposed to reduce the ripple current.
FIG. 3 shows a modification to the arrangement of FIG. 1, in which a circuit 44 is connected to the output of the correction stage 16. The circuit 44 includes a capacitor 42 having a first terminal connected to the line 24, and a resistor 40 having a first terminal connected to the second terminal of the capacitor 42 and a second terminal connected to electrical ground.
The current flowing in the circuit 44 provides information on the switching current flowing in the inductor 14. This information can be used to improve the switched power supply of FIG. 1 to remove at least some of the switching current in the generated power supply signal.
FIG. 4 illustrates a further modification to the arrangement of FIG. 3. A signal line 50 is connected from the circuit 44 - the connection point of the resistor 40 with the capacitor 42 - to the correction stage 16. The correction stage 16 thus receives, with this connection, information about the current flowing in the conductor 14 from the circuit 44. The signal on line 50 is a feedback signal to the correction stage.
The feedback signal to the correction stage utilises the characteristic that the voltage at the node between the resistor 40 and capacitor 42 in the circuit 44 provides information that is not otherwise available in the modulated power supply.
The feedback provided by the signal on line 50 can be made fast and can operate at high frequencies.
FIG. 5 shows a specific arrangement in which the feedback of the correction stage is used together with the feedback of the information on the switching current flowing in the inductor 14. The correction stage 16 is shown as additionally including an amplifier 54 and a feedback stage 52.
The correction amplifier 34 receives the feedback signal on line 50, and receives the output of the amplifier 54. The amplifier 54 receives the reference signal on line 20, and the output of the correction amplifier 34 fed back through a feedback stage 52. The feedback stage 52 applies any necessary attenuation to the feedback signal before it is applied to the amplifier 54. The feedback stage 52 and the amplifier 54 provide, in the arrangement of FIG. 5, the functionality of the feedback provided by the signal on line 19 in the earlier figures. The feedback provided on signal line 50 allows the signal generated by the correction stage 16, in the FIG. 5 arrangement the signal generated by the amplifier 34, to be adjusted to reduce the current ripple due to switching in the output signal, and hence lower the output impedance of the modulated power supply stage 28.
FIG. 6 shows an alternative arrangement. The combiner 36 of the FIG. 6 arrangement does not include a capacitor. The capacitor of the combiner of any previous figures may be eliminated in certain implementations, and FIG. 6 illustrates how the advantageous feedback connection may still be utilised even when the capacitor of the combiner is not implemented.
The switching stage and the correction stage are each shown as receiving a common reference signal. In embodiments they may receive different reference signals. In embodiments they may not both receive reference signals. The reference signal may indicate the ideal output signal. The reference signal may be the envelope of the RF input signal on line 4.
The circuit 44 may be provided for other purposes, and the invention may take advantage of the provision of this circuit for other purposes, to provide information which can be used to improve the switched power supply without adding additional circuit components, and just adding the connection of line 50. For example the circuit 44 may be provided to suppress resonance as disclosed in WO 2005/081399.
The capacitance value of the capacitor 42 and the resistance value of the resistor
40 will be implementation dependant.
The invention has been described with reference to example implementations. The invention is not limited to the specifics of any described embodiment, and any described element may be used individually or in combination within the scope of the appended claims.

Claims

CLAIMS:
1. A power supply comprising:
a switching stage;
a correction stage;
a combiner connected with an output of the switching stage and an output of the correction stage and configured to combine output signals of the switching stage and the correction stage to generate a power supply signal; and
a circuit connected with the output of the correction stage and configured to sense switching currents generated by the switching stage and flowing in the combiner.
2. The power supply of claim 1, wherein the circuit comprises a series connection of a resistor and a capacitor between the combiner and ground.
3. The power supply of claim 2, further comprising a connection from a junction of the resistor and the capacitor to the correction stage.
4. The power supply of claim 3, wherein the correction stage comprises an amplifier and is configured to modify the output signal of the correction stage in dependence on the connection.
5. The power supply of claim 4, wherein the correction stage is configured to modify the output signal of the correction stage further in dependence on a feedback connection from the output of the correction stage.
6. The power supply of any one of claims 2 to 5 in which the combiner comprises an inductor having one terminal connected with the output of the switching stage and a second terminal connected with the output of the correction stage, the circuit being connected with the second terminal of the inductor and the power supply signal being generated at the second terminal of the inductor.
7. The power supply of any one of claims 2 to 5, wherein the combiner comprises an inductor and a capacitor, the inductor having one terminal connected with the output of the switching stage and another terminal connected with one terminal of the capacitor, and wherein the capacitor has another terminal connected with the output of the correction stage, the circuit being connected with the second terminal of the capacitor and the power supply signal being generated at the second terminal of the inductor.
8. The power supply of any one of claims 2 to 5, wherein the combiner comprises an inductor, the circuit being configured to sense the switching currents in the inductor.
PCT/US2016/017515 2015-02-11 2016-02-11 Ac amplifier output impedance reduction WO2016130780A1 (en)

Applications Claiming Priority (2)

Application Number Priority Date Filing Date Title
GB1502248.6A GB2535180A (en) 2015-02-11 2015-02-11 AC amplifier output impedance reduction
GB1502248.6 2015-02-11

Publications (1)

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Cited By (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
WO2019026669A1 (en) * 2017-08-04 2019-02-07 株式会社日立国際電気 Wireless device and wireless output amplification method

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US20030137286A1 (en) * 2002-01-23 2003-07-24 Donald Kimball Capacitorless DC-DC converter
US20080258831A1 (en) * 2006-01-10 2008-10-23 Nec Corporation Amplifying apparatus
US20120194274A1 (en) * 2011-02-01 2012-08-02 Paul Fowers Integrated circuit, wireless communication unit and method for providing a power supply
US20130207731A1 (en) * 2012-02-09 2013-08-15 Skyworks Solutions, Inc. Apparatus and methods for envelope tracking
US20140028368A1 (en) * 2012-07-26 2014-01-30 Rf Micro Devices, Inc. Programmable rf notch filter for envelope tracking

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US20030137286A1 (en) * 2002-01-23 2003-07-24 Donald Kimball Capacitorless DC-DC converter
US20080258831A1 (en) * 2006-01-10 2008-10-23 Nec Corporation Amplifying apparatus
US20120194274A1 (en) * 2011-02-01 2012-08-02 Paul Fowers Integrated circuit, wireless communication unit and method for providing a power supply
US20130207731A1 (en) * 2012-02-09 2013-08-15 Skyworks Solutions, Inc. Apparatus and methods for envelope tracking
US20140028368A1 (en) * 2012-07-26 2014-01-30 Rf Micro Devices, Inc. Programmable rf notch filter for envelope tracking

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JINSUNG CHOI ET AL: "A Polar Transmitter With CMOS Programmable Hysteretic-Controlled Hybrid Switching Supply Modulator for Multistandard Applications", IEEE TRANSACTIONS ON MICROWAVE THEORY AND TECHNIQUES, IEEE SERVICE CENTER, PISCATAWAY, NJ, US, vol. 57, no. 7, 1 July 2009 (2009-07-01), pages 1675 - 1686, XP011258456, ISSN: 0018-9480 *

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* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
WO2019026669A1 (en) * 2017-08-04 2019-02-07 株式会社日立国際電気 Wireless device and wireless output amplification method

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GB201502248D0 (en) 2015-03-25
GB2535180A (en) 2016-08-17

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